The invention relates to apparatus for conveying melt (plastic material) from a plasticizer to injection molds. More particularly, the invention relates to improvements in so-called multiple-cavity stack molding apparatus wherein the means for conveying melt from the plasticizer comprises a plurality of injection nozzles or valves.
Apparatus of the above outlined character are used for simultaneous forming of plastic articles in several mold cavities. The injection nozzles are disposed between two sets of injection molds and are equipped with reciprocable needle-like valving elements (also called valve gate pins) which must be retracted in order to permit melt to issue from the orifices of the respective injection nozzles and extended in order to seal the respective orifices. The valving elements are reciprocable by pistons, and the apparatus further comprises a manifold which is provided with channels serving to supply melt to the nozzles. The manifold is heated, and the nozzles are installed in unheated platens of the manifold.
Certain heretofore known stack molding apparatus are designed in such a way that the injection nozzles for one set of molds are staggered with reference to injection nozzles for the other set of molds. This is necessary in order to take into consideration the length of valving elements and of the respective pistons as well as the dimensions of space which is available between the two sets of the injection molds. Attempts to assemble the injection nozzles into pairs of aligned nozzles include the provision of cylinder and piston drives which are adjacent the respective valving elements, and the utilization of levers for transmission of motion between the pistons and the valving elements. Neither of the just described conventional apparatus are entirely satisfactory for a number of reasons. Thus, the apparatus are bulky and comprise large numbers of parts. Moreover, the nozzles and the parts which are confined in the manifold are not readily accessible, and the assembly and dismantling times are too long. On the other hand, it is necessary to gain access to the injection nozzles and certain other parts at regular intervals in order to remove components which are subject to extensive wear, to repair the heating systems for the nozzles and/or for other reasons.
The aforediscussed proposal to employ pairs of aligned nozzles with their orifices facing in opposite directions is preferred at this time because the two sets of injection molds can be installed close to each other and the molds of one set can be mirror images of the molds of the other set. However, and since the cylinder and piston units which are used to reciprocate the valving elements of the injection nozzles must be placed next to the respective nozzles and must transmit motion by way of levers, the number of injection nozzles per unit area of the structure between the two sets of molds is relatively small. The number of injection nozzles per unit area of the structure between the two sets of molds is larger if the nozzles for one set of molds are staggered with reference to the nozzles for the other set of molds. However, this renders it necessary to employ two sets of different injection molds because the positions of inlets for admission of melt into the molds of one of the sets are different from the positions of inlets in the other set of molds. Moreover, neighboring nozzles must be maintained at a certain minimum distance from each other and each nozzle must extend across the full width of the structure between the two sets of molds.